The present invention relates to a method of treating H.sub.2 S containing gases. More particularly, the present invention relates to an improved method that can be implemented with a very compact equipment layout in performing the following process: an iron-oxidizing bacterium is allowed to grow in a fixed-bed type oxidation vessel so as to convert a solution of ferrous sulfate to a solution of ferric sulfate; H.sub.2 S in the gas to be treated is absorbed by the solution of ferric sulfate; the solution of ferrous sulfate that forms as a result of H.sub.2 S absorption is again oxidized with the iron-oxidizing bacterium to form another supply of a solution of ferric sulfate which is repeatedly used in absorbing H.sub.2 S in the gas being treated; and the sulfur content of the solution of ferric sulfate used as the H.sub.2 S absorbing liquor is fixed and recovered in the form of elemental sulfur (S.sup.0).
Bacterial oxidation of ferrous sulfate containing solutions has been accomplished for many years by such classical methods as the trickling filter process and the rotary disk process. In order to improve the efficiency of oxidation, methods are commercially used in which a dense population of iron-oxidizing bacteria that are adhered to iron precipitates or diatomaceous earth is retained in the oxidation vessel. See, for example, the disclosure in Japanese Patent Publication No. 38981/1972 entitled "Method of Continuous Oxidation of Fe.sup.2+ in Mine Water with Iron Oxides Containing an Iron-Oxidizing Bacterium" and U.S. Pat. No. 4,139,456, "Process for Oxidation Treatment of Fe.sup.2+ in wastewater", both having been filed an patented by the applicant of subject application.
Methods are also known to treat H.sub.2 S in gases with the solution of ferric sulfate produced by oxidation with iron-oxidizing bacteria, and they are disclosed in Japanese Patent Publication No. 21691/1986, "Method of Treating H.sub.2 S in Gases", and Japanese Patent Public Disclosure No. 21721/1986, "Method of Treating H.sub.2 S in gases", both having been also filed by the applicant of subject application.
The aforementioned conventional methods, in which iron-oxidizing bacteria are deposited on diatomaceous earth or other particulate matters that are suspended in solutions in the oxidation vessel, have the following disadvantages.
(1) A large-scale oxidation and a separation vessel (i.e., thickener) are necessary and this leads to the need to provide a very large installation area.
(2) The need to blow a large volume of air into the oxidation vessel leads to great power consumption.
The first problem is particularly serious in Japan where large quantities of H.sub.2 S have to be treated at oil refineries and other plants.